1. Field of the Invention
The present invention relates to a structure used in an ion beam irradiation apparatus to trap electrons within a magnet that deflects, scans, converges, or disperses ion beams.
2. Description of the Related Art
As one of the actions taken in response to a growing demand in recent years for improved productivity of ion beam irradiation apparatuses, focus is being placed on a technology for improving a transport efficiency of a low-energy ion beam having a positive charge. More specifically, a technology is available for suppressing a divergence of an ion beam that is passing through a magnet caused by a space charge effect by trapping electrons within the magnet used in the ion beam irradiation apparatus.
An example of such a technology is disclosed in Japanese Patent Application Laid-open No. 2008-521208 (Paragraphs 0020 to 0022, FIGS. 2 to 6) (hereinafter, “Patent Document 1”). Patent Document 1 discloses an analysis magnet that includes a plurality of magnetic field concentrating members arranged on opposing faces of magnetic pole members that are arranged.
The magnetic field concentrating members have ridges and grooves that produce a magnetic mirror effect inside the analysis magnet. Due to the magnetic mirror effect, when electrons moving along a magnetic field produced between the magnetic pole members approach one magnetic pole member, these electrons are reflected to the other magnetic pole member due to the influence of a concentrated magnetic field formed by the magnetic field concentrating members. Thereafter, the reflected electrons again move towards the first magnetic pole member along the magnetic field produced between the magnetic pole members. When the electrons approach the first magnetic pole member, these electrons are once again reflected in the opposite direction by the concentrated magnetic field of the magnetic field concentrating members. Thus, the electrons are trapped within the magnet by a combination of the movement of the electrons between the magnetic pole members and the reflection of the electrons by the magnetic field concentrating members.
However, even if the electrons are successfully trapped within the magnet according to the technology disclosed in Patent Document 1, the productivity of the ion beam irradiation apparatus cannot necessarily be improved merely by that alone.
Typically, the gap between the magnetic pole members is set keeping in view the size of the ion beam that is to be passed between the magnetic pole members, and is set slightly wider than the size of the ion beam. This configuration adapted to produce an adequately uniform magnetic field all over the ion beam.
Ion beams have a tendency to diverge due to a space charge effect. Therefore, even if divergence of the ion beam is suppressed by trapping the electrons within the magnet, the divergence cannot be suppressed completely, and there is always a slight divergence. Furthermore, even though an ion beam is perceived as a whole to travel in a straight line, the ion beam includes local beam components that travel in different directions. Therefore, a possibility of the ion beam colliding with the magnetic field concentrating members arranged on the magnetic pole members while passing through the gap between the magnetic pole members can be high.
Collision of the ion beam with the magnetic field concentrating members causes sputtering of the magnetic field concentrating members, resulting in their deformation. The deformed magnetic field concentrating members cannot produce sufficiently concentrated magnetic field, thus the trapping of the electrons deteriorates. To continue to maintain a good trapping effect, the deformed magnetic field concentrating members must be replaced with new ones. Because an operation of the ion beam irradiation apparatus needs to be stopped during replacement of the magnetic field concentrating members, the productivity of the ion beam irradiation apparatus drops.
Furthermore, the sputtering of the magnetic field concentrating members due to the ion beam causes the sputtered material to scatter as particles. If the magnetic field concentrating members are made of metal, the scattered metal particles of the magnetic field concentrating members contaminate the substrate that is to be irradiated by the ion beam, resulting in metal contamination, which is considered a fatal flaw in the manufacturing of semiconductor devises. This increases a failure rate of manufacturing of the semiconductor devises, resulting in a drop in the productivity of the ion beam irradiation apparatus.